White phlegm like stuff on lips (mouth!) during exercise?

I consider myself to be extremely healthy- I eat very well and exercise a lot, but whatever exercise I do (moderate walking or more extreme stuff like mountain biking and wakeboarding or at the gym) I get this line of white phlegm around my lips (I just have to emphasise I mean the lips on my mouth on my face not another more personal area!!) that you can pull off (like that stringy sleep you get in your eyes) this really bugs me as i'm sure it's pretty unsightly and my mouth feels all stuck together all the time, can anyone shed some light on this for me? thanks :)